Highland barley paper, a widely used material in electrical insulation, significantly affects its insulation properties in humid environments, with water absorption being a key factor contributing to insulation resistance degradation. In humid environments, water molecules from the air penetrate the interior of the highland barley paper through capillary action, diffusion, or direct adsorption. This process not only alters the material's physical structure but also significantly changes its electrical conductivity, leading to insulation resistance degradation.
Highland barley paper's moisture absorption process first manifests as surface adsorption. When relative humidity increases, a thin film of water forms on the material's surface. This film is inherently conductive, directly increasing surface leakage current and significantly reducing surface insulation resistance. For non-hygroscopic insulating materials, the surface water film may be thin and scattered, resulting in a relatively minor impact. However, as a porous material, highland barley paper often has a thicker, more continuous surface water film, resulting in a more pronounced degradation of surface insulation resistance.
As moisture absorption increases, water molecules penetrate further into the highland barley paper. The porous structure creates numerous microscopic channels within the material, allowing water molecules to diffuse deep into the material and be absorbed by the capillaries between fibers. During this stage, the volume insulation resistance begins to decrease. Internal moisture not only increases the conductive current but also promotes polarization, increasing the absorbed current. Consequently, when measuring insulation resistance, the total current decreases faster, shortening the time it takes for the insulation resistance to reach a stable value.
The effect of water absorption on the insulation resistance of highland barley paper is also reflected in changes in the conductivity mechanism. In its dry state, the conductivity of highland barley paper primarily relies on a small amount of impurity ions and weak currents between fibers. However, after absorbing moisture, water molecules, acting as polar molecules, align themselves in the electric field, forming conductive channels. Furthermore, moisture dissolves soluble impurities in the material, increasing the concentration of free ions and further reducing the resistance. Furthermore, high temperatures accelerate the movement of water molecules, enhancing conductivity. Therefore, the combined effects of temperature and humidity exacerbate insulation resistance degradation.
The hygroscopic properties of highland barley paper are also closely related to its material composition and structure. When cellulose insulation materials are near saturation, their insulation resistance exhibits an exponential relationship with relative humidity: the higher the moisture absorption rate, the faster the resistance decreases. Porous materials, due to their high internal and surface moisture absorption, experience significant reductions in both volume and surface insulation resistance. In contrast, non-hygroscopic materials such as paraffin wax and mica have a thin and scattered surface water film, making their insulation resistance less affected by humidity.
In practical applications, the insulation resistance decay pattern of highland barley paper follows this pattern: initially, the surface insulation resistance rapidly decreases due to the formation of a water film; subsequently, the volume insulation resistance gradually decreases as the internal moisture absorption increases. Finally, when the material reaches moisture equilibrium, the insulation resistance stabilizes, but at this point, its insulation performance has been severely compromised. Furthermore, if ambient temperature fluctuations cause condensation, the surface insulation resistance will further decrease sharply, accelerating the internal moisture absorption process, creating a vicious cycle.
To mitigate the insulation resistance degradation of highland barley paper in humid environments, the following measures can be taken: First, optimize the material formulation by adding hydrophobic additives or improving the fiber structure to reduce the material's moisture absorption rate; second, improve the manufacturing process, such as using vacuum impregnation to reduce internal porosity; and third, strengthen protection in the application environment, such as installing temporary shielding devices, controlling ambient humidity, or applying a moisture-proof coating to the material surface. These measures can help extend the service life of highland barley paper in humid environments and ensure the stable operation of electrical equipment.
